The killer also shot his partner, leaving her with serious gunshot wounds before taking his own life.

Gardai said the attack took place at about 6pm yesterday in the Mullach Alainn estate in Omeath, Co Louth, after officers answered a 999 call.

The gunman, in his mid 20s, was on bail awaiting trial for dissident republican terrorism.

Tributes to the dead garda were led by President Michael D Higgins, members of government and the Garda commissioner Noirin O'Sullivan.

"This most serious and tragic incident has not only led to the death of a member of An Garda Siochana, while on duty, but tragically has also involved the death of one and the serious injury of another person," President Higgins said.

"I want to express my deepest sympathy to the family and friends of the garda who has so tragically lost his life while responding to this incident. My thoughts at this time are also with all others who have been affected by the events in Omeath."

The commissioner was making arrangements to meet the dead garda's family.

"I am deeply saddened to hear of the death of my colleague in a fatal shooting incident this evening while carrying out their duties," Ms O'Sullivan said.

"At this time my thoughts and prayers and those of the entire Garda service are with his family, friends and colleagues.

"This incident highlights the unique nature of the job carried out by the men and women of An Garda Siochana, and the dangers they face every day."

The gunman had been on bail awaiting trial for IRA membership at the Special Criminal Court in Dublin after being arrested at the start of the year following a joint Garda-Police Service of Northern Ireland operation to target dissident republicans in the border area.

Justice Minister Frances Fitzgerald, said she was appalled by the loss of life.

"The fact that a garda has laid down his life while protecting the community is a cause of great sadness. His death will be mourned by the entire nation, grateful for the service which he gave to it," she said.

"Today's tragic events are a stark reminder of the risks which members of An Garda Siochana face day in day out trying to keep our communities safe.

"I know our communities will stand with An Garda Siochana at this most difficult time for them.

"While no words at this time can be expected to console his wife and children, his family, his colleagues and all who loved him, they know that he gave his life in the best traditions of An Garda Siochana protecting the community he was so proud to serve."

Door-to-door inquiries are expected to be conducted during the day as gardai attempt to piece together the events leading up to the shootings.

The dead garda is the 88th member of the force to be killed in the line of duty and the murder occurred in the same region of Co Louth where Detective Garda Adrian Donohoe was fatally shot on January 25 2013.

The Garda Representative Association (GRA) said it was shocked and saddened over the death of one of its members.

It offered thoughts and prayers to the officer's family, friends and colleagues.

GRA president Dermot O'Brien said: "This dreadful, dreadful news is the deepest fear of every police family. This puts everything we do into perspective.

"At this time of distress, the garda family will be doing everything possible to support the late garda's relatives and loved ones, friends and colleagues."

The leader of Ireland's Catholics, Archbishop Eamon Martin, spoke by phone from Rome to local priests.

"Like me they are very upset by this tragic incident which has devastated families and rocked the peaceful parish community in beautiful Omeath," he said.

"I ask for prayers for the recovery of the injured woman and for the families, friends and neighbours of those who have lost their lives. I encourage anyone who has information that can help the gardai with their investigation to come forward."

Niall Collins, justice spokesman for the main opposition party in Ireland, Fianna Fail, said he was shocked and offered condolences to family and colleagues and the Commissioner.

"Obviously details of this incident are still emerging but I am extremely shocked to hear that a member of An Garda Siochana has been killed tonight," he said.

Sinn Fein leader and representative for Louth, Gerry Adams, said he was shocked.

"My thoughts and sympathies are with the families of those who have died and have been injured," he said.

The Police Service of Northern Ireland also said thoughts were with counterparts in Ireland and Chief Constable George Hamilton said: "Thoughts are with our Garda colleagues. An officer paying the ultimate sacrifice in the line of duty."

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